Plasma Membrane

Phospholipid bilayer composition

polar hydrophilic heads on the outside

nonpolar hydrophobic tails on the inside

What is the phospholipid bilayer made of

• 3 Carbon glycerol

• 2 Fatty acid chains

• Phosphate group

Peripheral proteins

one side or the other

Integral proteins

permanently embedded into the membrane

transmembrane proteins

spans the entire plasma membrane

Fluid mosaic model

• the fatty acid tails cling together, so phospholipids in the presence of water form a self-sealing bilayer allowing breaks and tears in the membrane to heal themselves

• Membrane is viscous, allowing proteins to move freely enough to perform their functions without destroying the structure of the membrane.

• Proteins move to function

• Phospholipids rotate and move laterally

selective permeability

allows passage of some molecules but not all

• actively chooses which to let through using channels or proteins

how does the plasma membrane make ATP

the integral proteins act as enzymes that work in ATP production

semi-permeable membrane

lets molecules pass through based on physical size or solubility

simple diffusion

• a form of passive transport

• movement of a solute from an area of high concentration to an area of low concentration

• transports small molecules, such as oxygen and carbon dioxide, across the cell membrane

Facilitated diffusion

• a form of passive transport

• solute combines with a transporter protein in the membrane

• movement of ions or large molecules across the plasma membrane

• does NOT expend energy

Active transport

requires a transporter protein and ATP

• it expends/uses energy

• low concentration to a high concentration, so it goes AGAINST the concentration gradient

Osmosis

movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration

Osmosis: isotonic solution

no net movement of water occurs

Osmosis: hypotonic solution

water moves into the cell

• high solute concentration inside the cell

• low solute concentration outside the cell

• if the cell wall is strong, it contains the swelling

• if the cell wall is weak/damaged, the cell bursts (osmotic lysis)

Osmosis: hypertonic solution

water moves out of the cell

• low solute concentration inside the cell

• high solute concentration outside the cell

• causes the cytoplasm to shrink when water rushes out of the cell to dilute the high concentration outside (called plasmolysis)

plasmolysis

The shrinkage of a cell's cytoplasm away from the cell wall due to water loss by osmosis when the cell is placed in a hypertonic solution